1. Field of the Invention
The present invention relates to a laser device having a plurality of high-frequency power supplies, and more particularly to a laser device which, when one of the high-frequency power supplies fails, can separate the failing high-frequency power supply and be operated by the remaining normal high-frequency power supplies.
2. Description of the Related Art
Conventional laser devices have only one power supply for producing an electric discharge in the laser tube. When the power supply fails, therefore, the entire laser device is shut off.
The applicant has filed Japanese patent application No. 61-208492 on a laser device in which a laser tube has a plurality of electrodes associated respectively with high-frequency power supplies. FIG. 2 is a block diagram of the disclosed laser device. In a laser tube 10, a laser medium gas is circulated, an electric discharge is generated, and a laser beam is amplified. Designated at 12 is an output mirror, 13 is a total relection mirror, 14 is an air blower for circulating the laser medium gas, and 15 is a cooling unit for cooling the laser medium gas.
High-frequency power supplies (hereinafter referred to as RF power supplies) 21 through 28 are connected respectively to electrodes 31 through 38. Another electrode 39 is connected to ground. An output control circuit 41 enables the RF power supplies 21 through 28 according to output power required, which may be entered through a keyboard or the like. An output control line 42, shown as a single line, applies control signals to the respective RF power supplies to enable them respectively. Denoted at 51 is a laser beam.
Operation of the laser device shown in FIG. 2 will be described below. When the output power required may be half the full output power, signals are applied over the output control line by the output control circuit to enable the RF power supplies 23 through 26 while turning off the other RF power supplies. The current density in the central region in the laser tube is the same as that when the full output power is produced, and a TEM00 mode of operation is effected. However, the laser beam output is substantially proportional to the number of the enabled RF power supplies, and suitable for cutting off a workpiece, with a high oscillation efficiency obtained. By turning on some of the RF power supplies according to the output power needed, the desired output power can be produced without lowering the oscillation efficiency.
With a conventional laser device having a single high-frequency power supply, the laser device will be shut off if the power supply fails.
In a laser device with a plurality of high-frequency power supplies as shown in FIG. 2, when one of the high-frequency power supplies malfunctions causing its output voltage to be excessively increased or decreased, the laser device cannot be operated by the remaining high-frequency power supplies since these other normal high-frequency power supplies are connected to the laser tube parallel to each other.